Since at least the 1990's, nanoscale processes, structures, and devices have continued to become increasingly important in many fields, including electronics, biotechnology, and sensors. Sub-microscale fabrication processes can be broadly classed as ‘bottom-up’ processes that build structures from smaller components such as individual atoms and/or molecules, or ‘top-down’ processes that build small structures from larger entities. Top-down fabrication processes generally depend upon lithographic processes such as optical or electron beam lithography to define the lateral dimensions of microscale or sub-microscale features on a generally planar substrate or wafer. However, as the lateral dimensions of these features continue to decrease with technological and market needs, the lithographic processes and tools used to define these become increasingly expensive as the capabilities of each new generation of tools, in particular their spatial resolution, are stretched beyond the limits of the previous generation. Accordingly, leading edge tools and processes such as electron beam lithography, deep-UV and immersion optical lithography can be prohibitively expensive for many applications. Moreover, even where such tools are used, the yield of successfully fabricated structures or devices is typically quite low.
As an example, although conventional electronic-beam lithography has been employed to fabricate ultra-small separations between planar electrodes in electronic devices, nanometer length scale separation is still a challenge. Although very expensive lithographic tools and complex processes have been developed to fabricate transistors with ever-decreasing channel lengths, they are only able to cater for specific materials and processes and therefore cannot be generally applied to fabricate other types of structures having similar dimensions. In the field of molecular electronics, very complex processing schemes have been required to fabricate molecular transistors, and yet have only been able to produce extremely low yields of such devices.
It is desired to provide a fabrication process that alleviates one or more of the above difficulties, or at least that provides a useful alternative.